This invention relates to a circuit arrangement for controlling power supplied to a load, comprising a controllable self-conducting semiconductor switch connected in-series with a load.
The semiconductor switches used in power electronics, e.g., IGBTs, MOSFETs, thyristors or GTOs, are usually self-blocking. Semiconductor switches based on silicon carbide SiC have excellent properties making their use desirable in comparison with semiconductor switches based on silicon; this is because of their high dielectric strength, low resistance when conducting and their suitability for very high switching frequencies. Self-blocking switches based on silicon carbide SiC are not currently available commercially, however.
From ISPSD 2000—12th IEEE International Symposium on Power Semiconductor Devices & ICS, Toulouse, P. Friedrichs et al., “SiC power devices with low on-resistance for fast switching applications,” pp. 213-216, it is known that a self-conducting VJFET switch (VJFET =vertical junction FET) based on silicon carbide SiC can be combined with a self-blocking MOSFET to form a cascade, so that an electronic component which is self-blocking toward the outside is again obtained.
However, in applications, e.g., in a current supply in which a circuit arrangement for controlling the power supplied to a load is always supplied with power when it is at voltage, i.e., in operation, it is not absolutely necessary for a semiconductor switch used as a power switch in this circuit arrangement to be self-blocking. Instead, essentially a self-conducting controllable semiconductor switch may also be used alone in such applications. However, this leads to the problem that current begins to flow through the self-conducting semiconductor switch when the power supply of voltage is applied to the circuit arrangement. Therefore, there is the need for a trigger device for the self-conducting semiconductor switch to be operable within the shortest possible period of time, so that the trigger device can turn the switch off before the occurrence of an operating disturbance, e.g., an overload.